A cut-off control loop circuit in a television permits the automatic control of the cut-off point of the three RGB cathodes. The black level of the RGB signals is automatically adjusted to have the same cut-off current on each of the RGB cathodes, in order to have the proper DC level at each RGB cathode, for a correct colorimetry of low light level signals. The RGB cathode currents are sequentially measured at the output of the external video amplifier during the three cut-off lines. A conventional 8-bit digital cut-off control loop has low resolution of the black level adjustment requires a relatively long time to reach cut-off stability when the TV set is switched on, and cannot blank the RGB output when the cut-off control loop is not stable. To increase the resolution to 9-bits leads to even longer convergence times of the cut-off loops.